This patent specification relates to displaying radiological images and other information in a manner believed to assist users such as physicians in reading such images and other information. More specifically, it relates to a computer-aided diagnosis xe2x80x9cCADxe2x80x9d) system and method for detection and identification of abnormalities in radiological images, and to using the results to produce images that provide more useful diagnostic information and better patient care. The images can be viewed in conventional format but in conjunction with viewing an annotated road map of the location and/or the identification of suspected abnormalities found through computer processing of radiological images. The annotated map highlights and/or identifies suspected abnormalities to help the image reader better assess the presence and/or meaning and significance of abnormalities in the radiological image.
The utility of the system and method is further improved by initially acquiring an x-ray image that is low-contrast but wide-latitude (G=2.5, or G=2 or less). In the case of breast imaging, a low-contrast, wide latitude x-ray image makes it possible to include in the image significant information about both very dense and much less dense tissue whereas normal x-ray film (typically G=3) may not record sufficient information about dense breast tissue. On the other hand, a low-contrast image may not be as suitable for viewing, and laws and regulations may prohibit the use of film of G less than 3 for breast diagnosis. In a preferred embodiment, the low-contrast image is automatically processed in the electronic domain to find suspected abnormalities, taking advantage of the fact that the wide latitude may allows the film to contain more information than conventional images. Resulting information regarding such abnormalities is in turn used as a guide in automatically converting the initial, low contrast image to a display image that is high-contrast at areas of the suspected abnormalities, to thereby facilitate diagnosis and patient care.
The detection of abnormal anatomic regions in radiological images using a computer system comprising specialized software and possibly specialized hardware has been reported. For example, in the area of mammography, representative reports are: Giger et al in the May 1993 issue of RadioGraphics, pages 647-656; Giger et al in Proceedings of SPIE, Volume 1445 (1991), pages 101-103; Doi et al in U.S. Pat. No. 4,907,156; and Giger et al in U.S. Pat. No. 5,133,020. See, also, the disclosure of and in prior art cited in said parent applications. In particular, in the area of detecting spiculated or stellate lesions in mammograms using convergent line detectors as the principal abnormal feature detection algorithm, representative reports are: N. Karssemeijer in the book entitled xe2x80x9cDigital Mammographyxe2x80x9d, edited by A. G. Gale et al, published by Elsevier in 1994, pages 211-219; and Kegelmeyer et al in Volume 191 (1994) of Radiology, pages 331-337. In the area of detecting clusters of microcalcifications in mammograms using thresholding and a clustering kernel as the principal abnormal feature detection algorithm, representative report are: Nishikawa et al in Volume 20 (1993) of Medical Physics, pages 1661-1666; and Feig et al in Volume 33 (1995) of Radiological Clinics of North America, pages 1205-30. See, also, co-pending patent applications Ser. No. 08/676.660 filed on Jul. 10, 1966 entitled xe2x80x9cMethod and apparatus for fast detection of spiculated lesions in digital mammograms,xe2x80x9d and Ser. No. 08/901,541 filed on Jul. 28, 1997 entitled xe2x80x9cMethod and system for using local attenuation in the detection of abnormalities in digitized medical images.xe2x80x9d These two patent applications and each of the other references cited in this patent specification are incorporated herein by reference as though fully set forth herein. These systems are generally referred to as Computer-Aided Diagnosis (xe2x80x9cCADxe2x80x9d) systems, and are believed to be particularly useful to radiologists in the diagnostic process and particularly in screening radiological procedures. R2 Technology, Inc. of Los Altos, Calif. offers technology under the trade name ImageChecker and a system under the trade name ImageChecker M1000 to assist physicians in their review of screening mammograms by identifying image areas that might require further review. Information on this technology is available at www.r2tech.com.
In a screening radiological procedure, such as screening mammography, the patients typically are asymptomatic and true abnormalities (e.g. cancers) are said to occur at a typical rate of about one case per one hundred patient examinations. Reading of the mammograms, when most of them are negative, can be a tedious task that can make it difficult to maintain a constantly high attention level. Some detectable abnormalities can be missed or misdiagnosed, which can result in delayed or more costly treatment, and can even result in a reduction of patient""s longevity or chance of survival. According to an article in the May 26, 1993 issue of JAMA, pages 2616-2617, the misdiagnosis rate in mammograms can be in the range of 15 to 63%. The CAD system, serving as an electronic reminder or second reader, as a spell-checker can be in a word processor, can assist radiologists in attaining higher detection rate (higher sensitivity) for abnormalities or reducing the misdiagnosis rate (lowering the false-negative rate).
Applicant understands that a current procedure using a CAD mammographic system proceeds as follows. The physician views a radiological image, reaches a preliminary diagnostic decision, and then views a separate second image displayed on a CAD system. This second image is marked or annotated with a localized identification of the abnormalities that the CAD system has detected through computer analysis of a digitized version of the conventionally obtained radiological image. After a reexamination the area of the radiological image that corresponds to the position of the detected abnormalities displayed on the CAD system, the physician makes the final diagnostic decision. This final diagnostic decision may or may not be the same as the preliminary decision, depending on whether the physician found the additional diagnostic information provided by the CAD system to be significant and, if so, what significance the physician ascribed to it. Following the final diagnostic decision, and perhaps depending on the degree of suspicion for malignancy, the physician can recommend a course of further action, which can include no further action or further follow-up examinations or biopsy.
In the process of detecting abnormal anatomic features in radiological images using a CAD system as described in the above cited references, the radiological film image of a patient is processed through a film digitizer to generate a digitized image which is input as such into the system. The digitized image is then analyzed by a digital image processing computer with specialized software and perhaps also specialized hardware for abnormal anatomic feature detection. If abnormalities are detected, an annotated radiological image is displayed on a special TV monitor, with markers placed around or adjacent the detected abnormalities. This TV monitor typically has a large dimension (typically a screen diagonal of 12 inches or larger) and a high spatial resolution (typically more than 1000xc3x971000 pixels). Because of the large dimension and high spatial resolution, this TV monitor typically is positioned at some distance away from the film. Typically the center of the monitor is more than 12 inches from the center of the film on the conventional film illumination box. In addition, this special TV monitor typically has a low brightness and a high cost.
It is believed that the display method using a high-resolution TV monitor has certain shortcomings that make the process inconvenient and inefficient. The high-resolution TV monitor is expensive, its spatial resolution although high for monitors is still less than that of the original x-ray film, and its brightness and dynamic range are also inferior to those of an x-ray film viewed on a light box. Therefore, it is believed that a physician might not wish to rely solely on the image displayed on the TV monitor to make diagnosis, but typically would repeatedly go back to the conventional film illumination box to view the original film image. This can lead to the loss of valuable time and can be uncomfortable at least because of the different brightness levels and spatial resolution levels of the two images. In addition it is believed that diagnostic errors can arise from the need for the physician to shuttle back and forth between two different displayed images. Even when a potentially true abnormality (cancer) is detected and pointed out by the CAD system to the physician, the fatigue and eye discomfort and other effects due to viewing two images of such different characteristics may still cause the physician to miss the significance of the corresponding area on the original x-ray film and to fail to notice or appreciate the abnormal features of the detected abnormality and decide to ignore the detected abnormality.
Accordingly, one object of this patent specification is to provide an improved combined display of an x-ray radiological image and CAD-detected abnormalities from the x-ray image. A more specific object is to provide the CAD user with further processed, annotated and enhanced image representations of regions around the CAD detected abnormalities in order to emphasize abnormal image features of these detected abnormalities. Another more specific object is to produce an initial image that is low-contrast but wide latitude and use it to automatically find suspected abnormalities, and use information about the suspected abnormalities to automatically convert the initial image to a display image that is high-contrast at the density range of the found abnormalities. The ultimate goal is to help the user (physician) better assess the type and degree of abnormality of these detected abnormalities in the radiological image.
Another objective is to present the further processed image of the area around the CAD detected abnormalities on a display such as a small TV monitor located close to the x-ray film during viewing of the x-ray film. The term TV monitor is used generically, to refer to any type of electronic display, for example a flat panel display. The two images should be so close and should otherwise match each other such that eye and other discomfort due to viewing two different images alternately would be reduced. Still another object is to print the annotated road map and/or the further processed image representations of areas around the CAD detected abnormalities on the same sheet of photographic film that contains a printout of the radiological image.
This patent specification describes in detail, toward the end, the preferred embodiment that derives a low-contrast, wide latitude image, automatically extracts information about suspected abnormalities therefrom, and uses that information to automatically produce a display image that is high-contrast at the areas of the suspected abnormalities. Earlier parts of the patent specification describe embodiments involving primarily various ways to obtain an x-ray image, extract information regarding suspected abnormalities, and display that information in ways that facilitate diagnosis and treatment.
In an exemplary and non-limiting first embodiment, the further processed image of areas around the CAD detected abnormalities from a radiological film is presented on a small TV monitor, located in close proximity to the radiological film being viewed at the light box. The display of this further processed image shares (e.g., is toggled on) the small TV monitor with the display of a miniaturized annotated road map. On demand by the CAD user, e.g. the physician using a toggle switch, the miniaturized annotated road map image and the further processed image representations such as tiles of areas around the CAD detected abnormalities are displayed alternatively on the small TV.
In an exemplary and non-limiting second embodiment, the miniaturized annotated road map image is presented on a small TV monitor and further processed image tiles of areas around the CAD detected abnormalities are presented on a second and separate small TV monitor. Both small monitors preferably are located in close proximity to the radiological film being viewed at the light box.
In an exemplary and non-limiting third embodiment, the radiological image is acquired through digital means, and thus is in digital form initially. The radiological image can be displayed as an electronic image on a high-resolution monitor. The annotated map and, if desired the tiles as well, can be displayed on the same monitor, at an area that does not overlap with the areas of interest of the displayed radiological image. In some cases, the digitally acquired radiological image is printed on a sheet of photographic film for later viewing on a light box. In that case, the annotation road map and, if desired the tiles as well, can be printed on the same sheet of photographic film, at an area that does not obscure relevant parts of the radiological image.
In an exemplary and non-limiting fourth embodiment, a CAD system is used to enhance the informational content of image displays, by taking an initial radiographic image that has a low contrast but wide latitude. This allows imaging well on the same film or other imaging system of tissues that differ greatly in density. The initial image is processed to identify area of possible interest, such as areas of suspected abnormalities. Based on characteristics of these areas, the initial image is converted to a display image that has high contrast at the density range(s) of the already identified areas of possible interest and thus can provide enhanced diagnostic information and assist in any further treatment.